The present invention relates to tape reels applied to single-reel type magnetic tape cartridges, and, in particular, to a tape reel suitable for a magnetic tape cartridge of the so-called servo tracking system in which a servo signal is recorded in advance along a longitudinal direction of a magnetic tape, and signal recording and reproduction are performed while executing tracking control of a magnetic head array according to the servo signal, and to a magnetic tape cartridge for housing the tape reel.
Magnetic tapes have various uses for audio, video, computer data backup and so on. In the field of use for the backup tape, a magnetic tape, which has a storage capacity of not smaller than 200 GB per volume, has been commercialized in accordance with an increase in the capacity of the objective hard disk to be backed up. A backup tape of a large capacity exceeding 1 TB is scheduled in future, and the densification of the recording density will be further promoted. In order to cope with the densification of the recording density, the attempted conventional practices have been making the tape cartridge of a single reel, reducing the wavelength of the recording signal, narrowing the track pitch, adopting a servo tracking system and so on.
In the tape cartridge adopting the servo tracking system, a servo signal is recorded in advance along the longitudinal direction of the magnetic tape, and the signal recording and reproduction are performed while executing the tracking control of a magnetic head array according to the servo signal. The detailed practice includes the steps of guiding the magnetic tape by a read and write reference surface (hereinafter referred to as the read and write reference surface) of a tape guide provided for a tape drive while unwinding the magnetic tape outwardly of the main body casing at high speed, moving the magnetic head array in a direction perpendicular to the longitudinal direction (direction of run) of the tape on the basis of the servo signal of the magnetic tape, recording or reproducing a magnetic signal on a prescribed track and thereafter winding the tape at the same high speed as the unwinding speed.
As described above, in the tape system in which the recording signal has high density and the recording and reproduction of the signal are increased in speed, a phenomenon, which has posed no problem in the conventional tape system, causes a serious problem. When the magnetic tape is unwinded at high speed, one or several tape edges sometimes project from the wound tape layer due to the entrainment of air into the tape winding surface (this phenomenon being hereinafter referred to as edge projection). If the signal is recorded at high speed in the state in which the edge projection is occurring, the traceability of the magnetic tape, of which the edge has projected, to the read and write reference surface is poor, and the tracking by the servo signal cannot reliably be performed, consequently causing an output fluctuation due to the off-track error of the magnetic head array. In order to prevent the edge projection, the present invention has the tape receiving surface of the reel flange inclined toward the flange outer peripheral edge and further includes recess portions for preventing the entrainment of air, and the following prior arts are well known with regard to such reel structure.
When the magnetic tape is wound at high speed by the tape drive principally in a two-reel type magnetic tape cartridge, proposed methods have the practices of regulating the winding shape of the magnetic tape by forming an outwardly expanded spacing between the upper and lower flanges of the tape reel in order to orderly wind the magnetic tape around the tape reel (JP 2002-269711 A, Paragraph No. 0036, FIG. 2; JP 2002-83479 A, Paragraph No. 0030, FIG. 2; JP H06-282960 A, Paragraph No. 0005, FIG. 2; JP 2000-243054 A, Paragraph No. 0017, FIG. 1, etc.) and preventing the winding disorder by providing the flanges of the tape reel with air discharge paths (JP 2000-30401 A, Paragraph No. 0023, FIG. 1; JP H06-176532 A, Paragraph No. 0020, FIG. 1; JP 3003378 U, Paragraph No. 0016, FIG. 1) and so on.
JP 2002-269711 A is intended for the servo tracking system magnetic tape cartridge. There is provided a flange that serves as a reference of run in the single-reel type tape cartridge, and the spacing between the upper and lower flanges is set slightly greater than the width dimension of the magnetic tape. In JP 2000-30401 A, grooves for air discharge are alternately formed with the phase shifted in the rotational direction at each of the upper and lower flanges, and it is supposed that a two-reel type tape cartridge is described therein by a description of “handy VTR camera”.
In JP H06-176532 A, recess grooves for air discharge are provided on the inner surface of either one of the upper and lower flanges radially toward the flange outer peripheral edge. In JP 3003378 U, grooves for discharging air are provided on the inner surface of either one of the upper and lower flanges, and the opening area of the grooves are set not lower than 30% of the area within a range in which the magnetic tape is wound up. The tape cartridges of JP H06-176532 A and JP 3003378 U are two-reel type tape cartridges of a helical scan system.
In JP 2002-83479 A, as an example of the actual dimensions of the inclined surface of the flange, a difference in the height of the flange position between the flange inner peripheral edge side and the flange outer peripheral edge side is set to 0.02 mm to 0.46 mm. In JP H06-282960 A, the flange surface is inclined to set the difference dimension of the spacing between the flange inner peripheral edge side and the flange outer peripheral edge side to 0.18 mm or more in the single-reel type tape cartridge, and a window is formed at only the flange surface on the upper side, by which the tape is wound biased toward the lower flange.
As described hereinbefore, in the tape cartridge of the servo tracking system, the edge projection largely influences the reliability during the signal recording and reproducing. If the signal recording and reproduction are performed in the state in which the edge projection is occurring, the traceability to the read and write reference surface of the magnetic tape is degraded, and the tracking by the servo signal cannot surely be performed, consequently causing an output fluctuation due to the off-track error of the magnetic head array. The reduction in the-output during the recording and reproduction due to the off-track error significantly appears in the case of a high recording density tape of which the recording signal has a shortened wavelength and the track pitch has a narrowed width.
The present inventors considered that the winding disorder phenomenon observed in the conventional two-reel type tape cartridge was the cause of the off-track error and examined measures against the edge projection of the magnetic tape cartridge of the servo tracking system. However, as the result of detailed examinations and inspections, the inventors discovered that the output fluctuation due to the off-track error was large as shown in FIG. 15B when the edge projection occurred even though the winding shape of the magnetic tape was good and that the output fluctuation due to the off-track error was small as shown in FIGS. 15C, 15E and 15G when the edge projection did not occur even though the winding shape was bad. That is, the inventors found that the above phenomenon was the phenomenon peculiar to the magnetic tape cartridge of the servo tracking system and was not observed in the helical scan system of the normal two-reel type tape cartridge.
It is considered that the above phenomenon is presumably ascribed to the poor traceability to the read and write reference surface of the magnetic tape during recording and reproduction in the portion where the edge. projection occurs since the magnetic tape wound around the tape reel runs at high speed, as a consequence of which the magnetic head array cannot trace the servo track and causes the off-track error and the output fluctuation.
The edge projection as described above easily occurs when a magnetic tape is wound around a tape reel in the tape cartridge manufacturing process. The above is because the winding of the magnetic tape is performed at higher speed than during normal recording and reproduction (several times to several tens of times higher than during recording and reproduction). When the edge projection occurs, the tape suffers an unrecoverable damage as in a case where the projecting tape edge comes in contact with the flanges while being transported. Therefore, the edge projection has conventionally been prevented by setting the winding speed not higher than a specified speed (e.g., smaller than 10 m/sec) in the manufacturing process, and the manufacturing cost of the tape cartridge is increased by a time required for the winding of the magnetic tape. When the magnetic tape is repetitively used by the user, i.e., when the recording and reproduction are repetitively performed by a tape drive, edge projection similar to the aforementioned one sometimes occurs although not so frequently than in the manufacturing stage.
As described above, in the case of the tape cartridge for performing signal recording in the servo tracking system, it is required to achieve the winding of the magnetic tape around the tape reel at high speed without causing the edge projection by achieving high performance and high functions of the structures and mechanisms of, for example, a winder for winding a magnetic tape around a tape reel, a tape run mechanism of a tape drive, a cartridge structure, a tape reel around which a magnetic tape is wound and so on, to which less attention has been paid in a field of the conventional two-reel tape cartridge.